There have been micromirror structures to improve optical efficiency and motion efficiency with concealed underneath structure and appropriate flexure structure as in U.S. Pat. No. 6,028,689 to Michalicek, U.S. Pat. No. 6,906,848 to Aubuchon. The U.S. patent application Ser. No. 11/463,875 by Gim et al. also provides the other micromirror structure and design with more efficient motion and higher optical efficiency.
Since those micromirror structures are developed to have multi-axis rotation and translation motions, they require much complicated underneath structures to generate and control the required motions. Because of the complicated structure with more layers, more cost has to be paid for production. Even when those micromirror structures are arranged in an array, the prior art requires much complicated control methods to generate multi-axis rotation and translation, and they have small motion coverage because the system must be designed for any micromirror to cover full range of required motion.
Differently from the prior art having disadvantages and weaknesses of complicated structure and smaller motion coverage, the present invention has a lot of advantages such as low cost and structural stability thanks to the simplified structure, bigger motion coverage, and high efficiency in the micromirror motion and motion control.
The present invention contrives to solve the disadvantages of the conventional micromirrors with multi-axis rotational and translational motion.
The objective of the present invention is to provide a new structure for micromirror and the array of those micromirrors. The present invention also extends its advantages to the applications of the micromirror array which are disclosed in U.S. Pat. No. 6,396,619 to Huibers and U.S. Pat. No. 6,389,190 to Solgaard and Micromirror Array Lens, which is disclosed in U.S. Pat. No. 6,970,284 issued Nov. 29, 2005 to Kim, U.S. Pat. No. 7,031,046 issued Apr. 18, 2006 to Kim, U.S. Pat. No. 6,934,072 issued Aug. 23, 2005 to Kim, U.S. Pat. No. 6,934,073 issued Aug. 23, 2005 to Kim, U.S. Pat. No. 7,161,729 issued Jan. 09, 2007 to Kim, U.S. Pat. No. 6,999,226 issued Feb. 14, 2006 to Kim, U.S. Pat. No. 7,095,548 issued Aug. 22, 2006 to Cho, U.S. patent application Ser. No. 10/893,039 filed Jul. 16, 2004, U.S. patent application Ser. No. 10/983,353 filed Nov. 8, 2004, U.S. patent application Ser. No. 11/076,616 filed Mar. 10, 2005 and U.S. patent application Ser. No. 11/426,565 filed Jun. 26, 2006, all of which are incorporated herein by references.
With the newly introduced non-fixed underlying structure, the present invention makes possible for a micromirror array to have the same required optical surface profile by simple motion controls as that by complicated structure for multi-degrees of freedom motion, and improves structural stability, simplicity, flexibility, and efficiency in motion.
Generally, each micromirror of micromirror array must have multi-degrees of freedom motion to generate an arbitrary optical surface profile. When each micromirror has the same underlying structure and its orientation, each micromirror must have two degrees of freedom rotational and one degree of freedom translational motion in order to generate a desired optical surface profile. Moreover, to make an active light modulator to have variable focusing properties of Micromirror Array Lens, the micromirror array should generate multiple different motions with different surface profiles for corresponding light modulating properties or corresponding focal lengths for the Micromirror Array Lens. Thus, complicated underlying structure and control system should be present to have general motions with proper amount of translational and rotational coverage.
The basic idea of the present invention is to reduce this complexity. The complex motions with two degrees of freedom rotational and one degrees of freedom translational motion can be reduced simple one degree of rotational motion with proper arrangement of the underlying structures for motion generation. One additional degree of freedom translational motion optionally needed for general motion coverage.
According to Euler's Principal Rotation Theorem, any desired orientation can be simplified with one principal rotation of principal rotation angle. If this theorem is applied, multi-degrees of freedom rotational motion can be achieved by single principal rotation with provision of the proper structure arrangement. The motion generation structure should be arranged along the principal axis to have reduced degree of freedom motions.
In other words, the micromirror structure with one degree of freedom rotational motion optionally with degree of freedom translational motion can generate the desired motions with multi-degrees of freedom motion. It can be achieved with non-fixed underlying structure by arranging motion generation structures of each micromirror in the micromirror array to have single rotational motion about the principal axis and designing the underlying structure to generate and characterize one degree of freedom rotational motion optionally with one degree of freedom translational motion. Then, the structure of the micromirror array can be simplified and have effective usage with higher motion coverage and simple control system.
Also the micromirror array with non-fixed underlying structure can have simple control system. Even though the micromirrors in the array have different principal axes and different principal rotation angle. One common input signal can activate all the micromirrors in the array with different motions of rotation and translation even with different degrees of freedom. The present invention of the micromirror array with non-fixed underlying structure has simple control system and simple control method.
Thanks to the simplified and effective motion coverage of the micromirrors, the micromirror array can have reduced operational voltages. Since the structure is simplified, the gap between the electrodes for generating the operational force is reduced. So the operational voltage id considerably reduced.
The advantages of the present invention are not limited by the structure and system. Since the structures of the micromirror are simplified, fabrication process is reduced to simple. While making MEMS devices, the fabrication process is directly related to the yield rate. The present invention gives higher yield rate to fabrication since the structures and the fabrication processes are simpler than the micromirrors with fixed arrangement. The reduced processes for fabrication and higher yield produce higher cost effective devices.
The micromirror array with non-fixed underlying structure has many advantages such as much simpler motion generation structures, simple control system, simple control method, reduced operational voltages, simpler fabrication processes, higher yield, and cost effectiveness.